In the field of detecting radiation of different wavelengths, generally known as spectroscopy, it is conventional to use a dispersive element such as a diffraction grating, that disperses the radiation transversely to the direction of propagation. A straight forward approach to the problem of detecting the wavelength of incident radiation would be to use a diffraction grating and a set of photoelectric detectors placed at transverse locations corresponding to the commonly used laser wavelengths. Such an approach would certainly work, but it has the drawbacks of taking up a substantial amount of space and having the need to use electronic elements, with the associated requirement of a power supply.
The problem addressed by this invention is that of producing a compact optical spectroscopic detector that does not need electronics and can be read quickly by inspection to identify the wavelengths of the illuminating radiation.